1. Field of the Invention
The present invention relates generally to thermal sensors that detect the failure of mechanical devices when a predetermined temperature has been reached. More particularly, the present invention relates to thermal warning indicator that is used in place of an ordinary bolt of a railroad car bearing to indicate when the temperature of the beating has reached a level indicative of potential failure in the beating.
2. Description of the Prior Art
Warning devices are typically used to indicate a condition when a railroad car beating has exceeded a predetermined threshold temperature. This predetermined temperature is indicative of an approaching bearing failure. Such a warning device is necessary for the identification of bearing problems in order to avoid undesirable results, such as a train derailment. Responsive to such necessity, various warning devices have been proposed for detecting impending trouble of bearings before actual axle failure occurs. A detailed discussion of the background of such warning devices may be found in U.S. Pat. No. 4,812,826 to Kaufman, et al., issued Mar. 14, 1989.
It is known in the prior art that specially adapted bolts that are capable of indicating a warning condition may be used in place of the standard bolts for securing a bearing assembly. These special bolts can determine when a railroad car bearing reaches a predetermined threshold temperature, and indicate the overheating condition to a train crew in time to prevent potential problems. For example, the aforementioned U.S. Pat. No. 4,812,826 to Kaufman et al, provides a thermal sensor bolt having an electronic module that produces a warning signal. The module consists of a battery, switch, modulator, oscillator, and antenna that are combined to emit a radio frequency signal when the antenna moves through the middle of the module. When the thermal sensor bolt reaches a certain temperature, the antenna is moved, thus alerting a train crew to the possibility of a problem with the bearing.
One major problem with implementing a frequency generating module in standard axle cap bolt is the extreme sensitivity of electronic components to heat. In an environment where warning sensors are utilized, the temperature can rise as much as 250 degrees to 350 degrees Celsius. Not only do electronic components, such as modulators, oscillator and energy source, require a way to dissipate heat in order to function properly and reliably, but they must be shielded from extreme heat levels. Therefore, designing a warning device having a properly functioning frequency generating module has proven to be quite difficult.
A further problem concerns the switch mechanism that initiates the frequency generating operation of the module. Due to the harsh environment, and the high shock and vibration of train car bearings combined with the high temperature conditions, the switch mechanism must be solid and yet simple so as to remain reliable. In addition, the switch mechanism must be small and inexpensive such that their manufacture does not involve burdensome costs. Moreover, switch contact must be established only when the transmitter is intended to operate. Such switch mechanisms, like the frequency generating modules, have been difficult to implement in warning devices.
Accordingly, the present invention, unlike the prior art, recognizes these problems associated with frequency generating modules and energy sources in warning devices, particularly those envisioned for operation within standard axle cap bolts, and overcomes these problems without sacrificing reliability and undue material and assembly costs.
It is an object of the present invention to provide thermal sensor having a frequency generating means that is exposed to the least amount of heat possible under standard operating conditions.
It is another object of the present invention to provide a thermal sensor having a heat insulating element shielding the frequency generating means, including the energy source, from external heat emanating from the bearing assembly.
It is still another object of the present invention to provide a solid and reliable switch mechanism to activate the frequency generating means.